1. Field of the Invention
Aspects of the present invention relate to a method and apparatus for ultrasonic cleaning of a rigid substrate having an adhesive adhering to a surface thereof. The present invention particularly relates to a method and apparatus for ultrasonic cleaning off of a cured or uncured adhesive remaining on a rigid substrate after separating the rigid substrate laminate laminated with the adhesive.
2. Description of the Related Art
When a translucent rigid substrate of glass or the like is subjected to shape processing, glass in a sheet form has been cut and ground. However, a method of using an adhesive to laminate glass sheets into a multilayer laminate and collectively processing the laminate has been performed since the development of an adhesive for temporary fixing which allows the laminate to be separated by immersing it in hot water after bonding.
However, when air is mixed into the adhesive layer during the lamination and bonding, the UV light with which the adhesive is irradiated for curing decomposes and cleaves oxygen in the mixed air to generate oxygen radicals. The oxygen radicals inhibit the curing reaction of the adhesive, and the inhibited part remains uncured.
On the other hand, in the lamination of glass sheets, an ultraviolet-curable acrylic adhesive for temporary fixing is applied to glass sheets, which are stuck together and irradiated with UV light to thereby bond and laminate the glass sheets. When a printing pattern, a plating pattern, or the like through which UV light cannot easily transmit is applied to a glass surface, the degree of polymerization of the adhesive in the patterned part and adjacent parts thereof will be lower than that of the other parts, and the adhesive will be in an uncured state.
Generally, the adhesion of the adhesive to the glass is higher in the uncured part than in the cured part, and the adhesive components tend to remain on the glass in the subsequent step of separating the glass laminate and the adhesive to obtain glass sheets.
Moreover, even if the adhesive is in a cured state, the adhesive components may remain on the glass in the step of separating the laminated glass and the adhesive depending on the irradiance of the UV light applied for curing.
There is proposed a method of simultaneously oscillating at two different frequencies in a cleaning liquid stored in a cleaning tank in order to improve cleaning effectiveness (PTL 1). As the cleaning liquid, there are described a cleaning liquid mainly comprising a hydrocarbon-based solvent (hydrochloro=HC, hydrochlorofluorocarbon=HCFC) and a cleaning liquid mainly comprising an organic solvent (perfluorocarbon=PFC, hydrofluorocarbon=HFC).
There is proposed a cleaning method of immersion cleaning with a chemical solution followed by irradiation with ultrasonic waves in water (PTL 2). Further, it is stated that the chemical solution adhering to the surface of a substrate is scattered with heating. As the chemical solution, an acid or a mixed solution (POS) of sulfuric acid and aqueous hydrogen peroxide is described.
In order to enhance the cleaning effect, there is proposed a method of doubly arranging cleaning tanks to suppress uneven propagation of ultrasonic waves (PTL 3). There is stated that the cleaning liquid may be water or a cleaning liquid prepared by adding a surfactant to an acid or alkaline solution.